busybox test on qemu [almost pass]
except "free"

UART seems to work

kernel able to respond keyboard interrupt
==> UART can go to test
ADD: macro SIFIVE_B for board
ADD: dma [to be tested]

modify project structure for plic
ADD: pml.h && pml_hifive.h
"pml" is short for "physical memory layout"

implement an SD card driver based on SPI mode
I/O test [ok]
currently we do not support DMA mode

fix some bugs

ADD: spi I/O && sdcard driver [to be tested]
CURRENT BUG: stuck at "trapinithart"

modify directory structure of project
for platform specific code

consult -> [busybox_cmd_bak.txt]
for more information

Change the [tlock] field in the [proc] structure
spin lock ==> semaphore